Up to this time, only linear and five- or six-membered ring saccharides have been known as a saccharide moiety of a nucleoside constiting a nucleic acid. Recently, however, oxetanocin having a four-membered ring skeleton (oxetane ring) which is represented by the following formula: ##STR2## has been isolated from a natural substance for the first time as an aberrant constituent of a nucleic acid (see N. Shimada et al., J. Antibiotics, 39, 1623 (1986)).
The oxetanocin has antibacterial, antiviral and antitumor activities, so that it has been expected as a drug.
In order to facilitate the preparation of oxetanocin or various drivatives having the same saccharide moiety as that of oxetanosine, the development of a four-membered ring saccharide which serves as an intermediate for the preparation has been expected.